Plutonium

Plutonium is a rare radioactive, metallic and toxic chemical element. It has the symbol Pu and the atomic number 94. It is a fissile element used in most modern nuclear weapons. The most significant isotope of plutonium is 239Pu, with a half-life of 24,100 years. It can be made from natural uranium. The most stable isotope is 244Pu, with a half-life of about 80 million years, long enough to be found in extremely small quantities in nature, making 244Pu the nucleon-richest atom that naturally occurs in the Earth's crust, albeit in small traces.